At Memphis (map), Tennessee, the Mississippi crested late Monday at 47.8 feet (14.5 meters)—less than a foot below the city's record, set in 1937.

With the river now receding in the city and the rest of Shelby County, nature has "put the pin back in the grenade," said county spokesperson Steve Shular.

But explosive animal encounters may await returning evacuees.

"We're starting to see some issues, especially with the snakes," Shular explained. "We've definitely seen a lot of snakes, like water moccasins"—venomous pit vipers with potentially fatal bites that are also called cottonmouths (water moccasin picture).

With swollen rivers reaching up near homes and neighborhoods, "we want to make sure people understand that the rules have changed," Shular said.

"When that water gets into a neighborhood, snakes are going to be searching for shelter and food in homes or sheds or wherever they can slither into."

While most animals will survive the Mississippi River flood, for some their habitats could take years to return to normal, Odom said.

"Animals will be displaced for so long that, when the water does recede, it will take a while to get back to their original habitats," he said. "Some may be established elsewhere or displaced so far away that they never get back."

Finding food and shelter in the unfamiliar new surroundings could be stressful, Odom said. And the new neighbors may not exactly roll out the welcome wagon.

"Snake populations, in particular, could be really [threatened], because when they get into residential areas, people just destroy them," he said.

"Animals that appear to be in need of rescue should be left alone," Chad Harden, a big game coordinator with the agency, said in a May 6 statement.

"They are under stress, but their natural survival instincts will help them cope with the situation until things get back to normal. The animals could pose a real danger to someone who might try to rescue them."

For his part, Tennessee wildlife officer Odom is taking the long view.

"This isn't the first time we've seen major floods. It goes all the way back to Noah, and the animals are still here," he said. "The main thing is what humans will do to let them come back."